The instance will be rebooted (on new hardware if necessary) but will retain its Instance Id, IP Address, Elastic IP Addresses, EBS Volume attachments, and other configuration details.

而被限制在比較新的硬體上，並且目前只有 us-east-1 有：

This feature is currently available for the C3, C4, M3, R3, and T2 instance types running in the US East (Northern Virginia) region; we plan to make it available in other regions as quickly as possible.